ABSTRACT Despite anecdotal evidence suggesting conscious states in a variety of non-human animals, no systematic neuroscientific investigation of animal consciousness has yet been undertaken. We set forth a framework for such an investigation that incorporates integration of data from neuroanatomy, neurophysiology, and behavioral studies, uses evidence from humans as a benchmark, and recognizes the critical role of explicit verbal report of conscious experiences in human studies. We illustrate our framework with reference to two subphyla: one relatively near to mammals - birds - and one quite far -cephalopod molluscs. Consistent with the possibility of conscious states, both subphyla exhibit complex behavior and possess sophisticated nervous systems. Their further investigation may reveal common phyletic conditions and neural substrates underlying the emergence of animal consciousness.

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Animal Consciousness: A Synthetic Approach 1 2 David B. Edelman1 & Anil Seth2 3 1The Neurosciences Institute, 10640 John Jay Hopkins Drive, 4 San Diego, CA 92121, USA 5 david_edelman@nsi.edu 6 7 2Department of Informatics, University of Sussex, Brighton BN1 9QJ, UK 8 a.k.seth@sussex.ac.uk 9 10 Abstract 11 Despite anecdotal evidence suggesting conscious states in a variety of non-human 12 animals, no systematic neuroscientific investigation of animal consciousness has yet been 13 undertaken. We set forth a framework for such an investigation that incorporates 14 integration of data from neuroanatomy, neurophysiology, and behavioral studies, uses 15 evidence from humans as a benchmark, and recognizes the critical role of explicit verbal 16 report of conscious experiences in human studies. We illustrate our framework with 17 reference to two subphyla: one relatively near to mammals—birds—and one quite far—18 cephalopod molluscs. Consistent with the possibility of conscious states, both subphyla 19 exhibit complex behavior and possess sophisticated nervous systems. Their further 20 investigation may reveal common phyletic conditions and neural substrates underlying 21 the emergence of animal consciousness. 22 23 (terms in bold appear in the glossary) 24 25 26

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A synthetic framework for studying animal consciousness. 26 27 Although Darwin proposed that animal and human minds alike are the products of natural selection 1, questions of animal consciousness were largely neglected throughout the 20th century (but see Griffin2; note the term ‘animal’ is used here to mean ‘non-human 28 29 30 animal’). This neglect may have arisen in part because, seemingly, only humans are 31 capable of accurately describing their phenomenal experience. However, there is now 32 abundant and increasing behavioral and neurophysiological evidence consistent with, and 33 even suggestive of, conscious states in some animals. We will use humans as a 34 benchmark for the development of new empirical criteria for further investigation. Here, 35 we apply this approach to birds and cephalopod molluscs, subphyla that exhibit complex 36 cognitive faculties and behaviors and have strikingly elaborate brains. These two 37 subphyla are examples of highly distinct lineages, and their study provides an excellent 38 opportunity to examine how conscious states might be instantiated in very different 39 nervous systems. While we do not resolve this issue here, we propose that its 40 examination lies within the reach of contemporary neuroscience. 41 42 Humans as a benchmark. The notion that consciousness can be engendered in 43 different nervous systems by a variety of underlying mechanisms suggests a need to 44 examine constraints, and therefore to synthesize behavioral, neurophysiological, and 45 neuroanatomical evidence. Human studies involving the correlation of accurate report 46 with neural correlates can provide a valuable benchmark for assessing evidence from 47 studies of animal behavior and neurophysiology. A constraint on this strategy is that the 48 capacity for accurate report of conscious contents implies the presence of higher-order 49 consciousness, which in advanced forms may require linguistically-based narrative 50 capability. This is in contrast to primary consciousness, which entails the ability to create a scene in the ‘remembered present’3 in the absence of language. Primary 51 52 consciousness may be a basic biological process in both humans and animals lacking true 53 language. 54 Various properties of human consciousness can be identified at neural, behavioral, and phenomenal levels 4. Neural correlates of human consciousness include the presence 55 56

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of thalamocortical signaling, fast, irregular, low-amplitude electroencephalographic (EEG) signals, and widespread cortical activity correlated with conscious contents 5-7. At the behavioral level, consciousness has been associated with behavioral flexibility 8, rational action 9, and certain forms of conditioning 10. These can be related to cognitive properties involving widespread access and associativity 8, multiple discriminations 11, and the capacity for accurate report 5. These properties can be mapped to a variety of functions related to consciousness 12. At the phenomenal level, human consciousness 57 58 59 60 61 62 63 involves the presence of a sensorimotor scene, the existence of a first-person perspective, the experience of emotions, moods, and a sense of agency 13 14. 64 65 Using humans as a benchmark, behavioral, cognitive, and neural properties can be 66 employed as empirical criteria informing the ascription of conscious states to animals 67 (Figure 1). The application of this approach requires that: (i) at least some of these 68 properties reliably occur in both humans and animals; (ii) human brain areas responsible 69 for consciousness can be seen to be integrated with those areas responsible for accurate 70 report of phenomenal experience; and (iii) neural evidence that can be correlated with 71 phenomenal properties of consciousness must in addition account for those properties. 72 73 In humans, explicit verbal, or linguistic, report of a conscious experience is 74 sometimes taken as a ‘gold standard’ in the sense that it guarantees the presence of 75 consciousness. However, many creatures, including infants, most animals, and aphasic 76 human adults, are constitutively unable to produce linguistic reports. The production of 77 such reports is therefore too limiting a criterion for ascription of consciousness in general. 78 Importantly, accurate report may exploit behavioral channels other than language, for 79 example lever presses or eye blinks (Box 1). However the ability to provide such report 80 nonetheless implies the presence of higher-order (metacognitive) access to primary 81 conscious contents, which may not be constitutively required for primary consciousness. 82 Our approach therefore recognizes that the mechanisms responsible for primary 83 consciousness may be distinct from those mechanisms enabling its report. 84 85

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The extent to which neural evidence can account for phenomenal properties is 86 particularly important with respect to those properties that are common to most or all 87 conscious experiences. For example, in humans, every conscious scene is both integrated (i.e., ‘all of a piece’) and differentiated (i.e., composed of many different parts) 11. 88 89 Therefore, finding neural processes that themselves exhibit simultaneous integration and 90 differentiation would help to explain, and not merely correlate with, the corresponding 91 phenomenal property. Such neural processes can therefore be considered to be ‘explanatory correlates of consciousness’ 14 , and because they are explanatory, their 92 93 identification in animals is more suggestive of the presence of corresponding phenomenal 94 properties than is the identification of neural correlates per se. In this view, conscious 95 states are neither identical to neural states nor are they computational or functional 96 accompaniments to such states; rather, conscious states are entailed by neural states in 97 much the same way that the spectroscopic response of hemoglobin is entailed by its molecular structure 6. 98 99 100 The presence of voluntary behavioral responses is another candidate ‘gold 101 standard’ for the ascription of consciousness. However, the absence of such responses in 102 humans does not necessarily imply absence of phenomenal experience. For example, in a 103 recent study of a patient in a behaviorally unresponsive vegetative state, brain activity related to volition was taken as persuasive evidence of residual consciousness 15. 104 105 Conversely, behavior that appears to be volitional could be attributed widely among 106 animals on the basis of spontaneous and adaptive behavioral responses. Therefore, 107 apparent voluntary behavior at best provides a weak criterion for the ascription of 108 consciousness. In addition, conditions such as the vegetative state underscore the point 109 that consciousness should not be confused with arousal or inferred directly from the 110 existence of distinct sleep/wake cycles. States resembling deep sleep have been observed in many animals, including Drosophila melanogaster 16 and Caenorhabditis elegans 17; conversely, female killer whales and dolphins and their newborn calves may not sleep for periods of four to six weeks postpartum 18. 111 112 113 114 115

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Mammalian consciousness: Extending the benchmark. Mammals, particularly 116 primates, share with humans many neurophysiological and behavioral characteristics 117 relevant to consciousness, and therefore represent a relatively uncontroversial case for the ascription of at least primary consciousness 5. In a classical example, Logothetis et al. 118 119 trained rhesus macaque monkeys to press a lever to report perceived stimuli in a binocular rivalry paradigm 19 (Box 1). Neurons in macaque inferior temporal (IT) 120 121 cortex showed activity correlated with the reported percept, whereas neurons in the visual 122 area V1, instead responded to the visual signal. This suggests a critical role for IT in 123 visual consciousness. These observations are consistent with evidence from humans 124 subjected to binocular rivalry while being examined via magnetoencephalography 125 (MEG). The results from these studies suggest that consciousness of an object involves widespread coherent synchronous cortical activity 20. This correspondence between 126 127 monkeys and humans provides an example of how benchmark comparisons across 128 humans and animal species can be made. With this in mind, we now explore the 129 application of benchmark comparisons to two widely divergent animal subphyla: birds 130 and cephalopod molluscs. We are aware of the pitfalls of making facile comparisons and 131 implying that homologies exist in the absence of strong evolutionary evidence. In each 132 case, we will present behavioral evidence first, and then present evidence based on neural 133 architecture and dynamics. 134 135 Building a Case for Avian Consciousness 136

Avian cognition and behavioral capabilities. Feats of avian memory 21, 22, tool use and manufacture 23 , deception 24, and vocal learning and performance 25, 26, the capacity of some species to employ lexical terms in meaningful ways 27, and evidence for higher order discriminations in some birds 27, 28 collectively support the functioning of nervous 137 138 139 140 141 systems as sophisticated as those of most mammals. 142 143 Episodic and working memory capabilities are implied by the sophisticated food caching behaviors of corvids (e.g., jays, jackdaws, magpies, rooks, crows, and ravens) 23 144 145 and by laboratory-based demonstrations of transitive inference and delayed-match-to-146

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sample in pigeons and great tits 29. African grey parrots, magpies, and ring doves have 147 shown the ability to track periodically hidden and displaced objects; such object constancy certainly requires working memory 30. In addition, spatial learning, though 148 149 obviously implied by navigation during flight, has been shown explicitly by hooded crows learning to negotiate a radial maze 31. 150 151 152 Studies of avian tool use and manufacture imply not only elaborate memory and 153 learning substrates, but also the ability to make sophisticated discriminations and to plan 154 behaviors before executing them. For example, New Caledonian crows have been 155 observed to fashion hooked-wire tools to retrieve food from a glass cylinder, sometimes flying to a distant perch to bend the wire before returning to the cylinder 23. Similarly, 156 157 wild crows are known to fabricate tools from twigs and leaves in order to extract insects from holes in trees 23. In addition, a variety of avian species, including Japanese quails32 and European starlings 33, may be capable of social or observational learning (but see Zentall 34 and Heyes 35). Perhaps most notable are instances in which scrub jays re-cached food in private after their initial caching was witnessed by conspecifics 30, and 158 159 160 161 162 observations of ravens challenging conspecifics that witnessed caching activities while ignoring ‘naïve’ birds 36. These behaviors suggest that some birds may be capable of 163 164 theory of mind. 165 166 The avian vocal channel. While the foregoing cognitive capabilities are suggestive of 167 conscious states, the most promising avenue for investigating avian consciousness may 168 involve the study of species capable of vocal learning, which enables a highly flexible 169 form of accurate report. The capacity for some form of vocal learning is shared by at 170 least six animal groups, including cetaceans, bats, parrots, songbirds, hummingbirds, elephants, and possibly even mice and some other rodents 37. In birds, vocal learning 171 172 enables sophisticated song learning and production, mimicry of sounds, and, in the psittacines (parrots), word production, comprehension, and naming 27. For example, 173 174 African grey parrots were able to name objects, having acquired vocabularies roughly 175 equivalent to those of some language-trained chimpanzees (albeit after years of training and reinforcement) 38. Indeed, by naming objects in categorization paradigms, these 176 177

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animals appeared to produce accurate reports of sophisticated discriminations they were 178 making. ‘Alex,’ a principal subject of many of these experiments, when presented with 179 an altered array of objects, seemed able to make a judgment to the effect that, ‘‘I know 180 that something in this perceptual scene has changed, and here is what has changed.’’ 181 This finding suggests the ability to make discriminations about putative primary conscious states that appears to resemble some form of higher order consciousness 27 28. 182 183 184 185 Avian neural structures and processes homologous to those of mammals suggest 186 possible neural substrates for both consciousness and its report. 187 188 On what structural bases might avian vocal behavior be related to structures 189 underlying human verbal accurate report? Supporting evidence could come from shared 190 neural mechanisms. One example may be the neural substrate for motor learning in 191 mammals and that for song learning in some birds. Much of the neural basis for song 192 learning in oscines (songbirds) and psittacines resides in an anterior forebrain pathway involving the basal ganglia, in particular, a striatal nucleus called Area X 39 (see Figure 193 194 2). The anatomical and physiological properties of neurons in Area X closely resemble 195 those of neurons in the mammalian striatum. Specifically, the four neuronal phenotypes 196 found in mammalian striatum are also present in Area X. A notable difference is the 197 presence of a fifth neural phenotype in Area X—but not in mammalian striatum—that is 198 similar to cells found in the mammalian globus pallidus. Area X may therefore comprise 199 a novel mixture of striatal and pallidal anatomies, but it is nonetheless recognizably 200 homologous to the direct striatopallidothalamic pathway of the mammalian basal ganglia 201 39. A similar circuit has been reported in the anterior forebrain of the budgerigar, a parrot 202 40. Together, these findings strongly suggest common functional circuitry underlying the 203 organization and sequencing of motor behaviors related to vocalization in birds and 204 mammals capable of vocal learning. However, whether in some birds this circuitry is 205 embedded within a broader network homologous to that underlying human verbal report 206 remains to be determined. 207 208

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Another avenue for exploring non-mammalian consciousness is to identify 209 structural and functional homologs to mammalian thalamocortical systems. Vertebrate 210 nervous systems follow a highly conserved body plan that emerged with the first 211 chordates more than 500 million years ago. Consequently, many vertebrate neural 212 structures can be traced to common origins in specific embryological tissues. Avian 213 homologs of subcortical structures, such as the hypothalamus and pre-optic area, are 214 relatively easy to recognize. Although the identity of the avian neural homolog of mammalian isocortex remains controversial 41, 42, comparative embryological studies 215 216 suggest that the basic underlying neuronal composition and circuitry of the mammalian 217 cortex were established within clustered arrangements of nuclei long before the appearance of the distinct six-layered mammalian cortex 43. In particular, the nuclei 218 219 comprising the dorsal ventricular ridge (DVR) of the developing avian brain contain 220 neuronal populations homologous to those present in different layers of the mammalian 221 neocortex. These include neurons receiving thalamic input, as well as cells projecting to 222 brainstem and spinal cord neurons. The neurons of the avian DVR and mammalian 223 cortex are nearly identical in both their morphology and constituent physiological properties 44. 224 225 226 Structural homologies can also be identified using molecular and 227 immunohistological techniques. In particular, neurotransmitters, neuropeptides, and 228 receptors specific to particular neuronal populations within mammalian brain regions 229 have been localized to homologous avian brain regions. For example, both AMPA 230 receptor subunits and the pallidal neuron/striatal interneuron marker Lys8-Asn9-231 neurotensin8-13 (LANT6) are found in the neurons of both mammalian and avian basal ganglia 45, 46. Finally, gene expression patterns similar to those of mammals have been 232 233 identified in the avian brain. For example, a comparison of homeotic genes involved in 234 early brain development in chick and mouse embryos has revealed robust structural homologies between parts of the avian telencephalon and mammalian cortex 47. 235 236 237 Deep avian-mammalian homologies have also been revealed by examining 238 functional properties of neuronal populations within particular brain regions. The avian 239

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anterior forebrain pathway may be functionally analogous to the mammalian corticobasal 240 ganglia–thalamocortical loop. This is suggested by the presence of both inhibitory and 241 excitatory pathways in the medial nucleus of the avian dorsolateral thalamus (DLM), as 242 well as by functional similarities between neurons in the DLM and mammalian 243 thalamocortical neurons. Similarities have also been found among the excitatory and 244 inhibitory circuitry of birds and mammals, particularly in the serotonergic, GABAergic, and dopaminergic systems 48. 245 246 247 In addition to neuroanatomy, electrophysiological studies are critical in 248 establishing functional homologies between avian and mammalian nervous systems. 249 Currently, however, common properties of mammalian thalamocortical neurons, such as 250 low-threshold calcium (Ca2+) spikes and slow oscillations, have not yet been found in birds 49. Nonetheless, similarities between the waking EEG patterns of birds and mammals, as well as slow wave electrical activity recorded during avian sleep 50, are 251 252 253 suggestive of neural dynamics that might support conscious states in birds. 254 255 The existence in birds of structural and functional homologies to mammalian 256 thalamocortical systems is certainly consistent with the presence of higher cognitive faculties and perhaps consciousness 30, 51. Nevertheless, a compelling case for avian 257 258 consciousness cannot be made solely on the strength of relevant neuroanatomical and 259 neurophysiological resemblances. Nor are descriptions of avian behaviors that imply 260 sophisticated cognitive capabilities sufficient to make such a case. New experimental 261 strategies are needed for evaluating possible conscious discriminations in awake, 262 behaving birds. The findings obtained from studies of Alex the African grey parrot 263 encourage the development of such strategies. Even more challenging though are 264 approaches to investigating conscious behavior in invertebrates. 265 266 Searching for Consciouness in Invertebrates: The Cephalopod Case 267 268 The richness of cephalopod behavioral repertoires. In addition to possessing large 269 brains, cephalopod molluscs have extremely flexible behavior and highly developed 270

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attentional and memory capacities that may be suggestive of conscious states 52. The 271 performance of some cephalopods (particularly Octopus vulgaris) in several learning and memory paradigms (e.g., flexibility, persistence of memory traces, contextual learning)53 272 273 is formidable, and comparable in sophistication to that of some vertebrates. Octopuses can make discriminations between different objects based on size, shape, and intensity 54, 274 275 55, classifying differently shaped objects in the same manner as vertebrates ranging from goldfish to rats 55. Octopuses are also capable of finding the correct path to a reward in a plexiglas maze and can retrieve objects from a clear bottle sealed with a plug 56, 57. In 276 277 278 another striking study, ‘naïve,’ or ‘observer,’ octopuses watched conditioned animals 279 (‘demonstrators’) choose between two simultaneously presented objects that differed in 280 contrast only; the observer octopuses later made the same contrast choices in isolation and without any explicit conditioning 58. Although controversial 59-62, this finding 281 282 suggests that octopuses are capable of observational learning, a faculty previously 283 thought to be unique to highly social animals. 284 285

both the octopus and the cuttlefish 53, 63. In a maze containing obstacles that were Finally, distinct capacities for short- and long-term memory have been shown in 286 287 changed ad libitum; octopuses could remember these changes and adjust their movements 288 accordingly. Interestingly, the octopuses in this study appeared to pause and deliberate about the layout of the maze before proceeding 64. 289 290 291 Cephalopod brains: complex nervous systems distant from the vertebrate line. The 292 organization of invertebrate nervous systems diverges so greatly from those of 293 vertebrates such as birds and mammals that, until recently, sophisticated cognitive capabilities had rarely been ascribed to invertebrate species (see Figure 2). Bees 65, 66, spiders 67 68, and the cephalopod molluscs 52 are notable exceptions. 294 295 296 297 Of all cephalopod molluscs, the octopus has the largest population of sensory 298 receptors. These receptors communicate with a nervous system that, in adults, may contain between 170 million and 500 million cells, most of which are neurons 69, 70. In 299 300 the brain of one genus of squid, Loligo, at least 30 distinct nucleus-like lobes have been 301

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identified 71. The optic lobe, the largest of the fused central ganglia, contains as many as 302 65 million neurons. In addition to processing visual input, the optic lobe plays a critical role in higher motor control and the establishment of memory 69. A number of other lobes may be functionally equivalent to vertebrate forebrain structures 69, though their 303 304 305 organization bears little resemblance to the laminar sheets of mammalian cortex. In 306 particular, the vertical, superior frontal, and inferior frontal lobes of octopus, squid, and cuttlefish are involved in memory consolidation 63, 72, 73. In experiments in which the 307 308 vertical lobe of Octopus vulgaris was lesioned, the ability to learn visual discriminations was severely impaired, but long-term memory consolidation remained intact 63. Removal of the median inferior frontal lobe caused memory deficits that compromised learning 54, 309 310 311 74. Taken together, these studies suggest that some regions of the octopus frontal and vertical lobes are functionally comparable to regions of mammalian cortex (see Young 75 312 313 for a review). 314 315 Radical differences between cephalopod nervous systems and those of vertebrates 316 are exemplified by the parallel, distributed architecture of the octopus locomotor system. 317 The number of neurons in the tentacles of the octopus collectively exceeds the total number in the central fused ganglia of the brain itself 70. A detached octopus arm will flail in a realistic manner when stimulated with short electrical pulses 76, suggesting 318 319 320 pseudoautonomous control of some locomotor behavior patterns and hinting at a 321 sophistication of sensorimotor coordination rivaling that of many vertebrates. This 322 elaborate bodily representation in the service of sensorimotor coordination for adaptive behavior (e.g., locomotion, camouflage, mimicry) might support a ‘core selfhood’ 77 (see 323 324 Box 2), a tantalizing concept as applied to cephalopods. 325 326 With regard to neuropharmacological and physiological properties, the 327 cephalopod nervous system contains many of the major neurotransmitters that are found in mammalian brains69, 78. In particular, the presence of dopamine (DA), noradrenaline 328 329 (NA), and serotonin (5-HT) receptor subtypes that resemble those found in vertebrates 330 may reflect the presence of circuitry similar to vertebrate excitatory and inhibitory 331 pathways. As is the case with functional avian neuroanatomy, application of 332

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immunohistochemical and genetic techniques may help determine cephalopod functional 333 analogs to neural regions in mammals that show correlated activity during conscious 334 behavior. An encouraging indication is the recent identification of a cephalopod ortholog 335 to the FoxP2 gene, which in birds and humans has been implicated in motor function 336 related to song and language production, respectively. Notably, FoxP2 expression has been observed in the adult octopus chromatophore lobes79. 337 338 339 What can be said of neurodynamics in cephalopod brains? Examination of 340 octopus vertical lobe slices has identified long-term potentiation (LTP) of glutamatergic synaptic field potentials similar to those found in vertebrates 80. More directly related to 341 342 possible conscious states, electrophysiological studies have identified EEG patterns, 343 including event related potentials, which resemble those of awake vertebrates, and at the same time are distinct from those recorded in other invertebrates.81, 82. Identifying 344 345 cephalopod EEG patterns that reflect low amplitude fast irregular activity similar to that 346 observed during human conscious states will require determination of suitable recording 347 sites. Optic, vertical, and superior lobes of the octopus brain—all of which are critical to 348 learning and memory—are relevant candidates. 349 350 The similarities discussed above by no means confirm the existence of conscious 351 states in cephalopod molluscs, but neither do they exclude them. An intermediate effort 352 to clarify the situation might be the pursuit of psychophysics in cephalopods, an approach 353 not yet represented in the literature (see Box 1). 354 355 Concluding remarks. Approaches to animal consciousness require both clear theoretical 356 frameworks and relevant experimental evidence. We have suggested that a useful 357 approach is to synthesize neuroanatomical, neurophysiological, and behavioral evidence, 358 using humans as a benchmark. We recognize that a distinction between primary and 359 higher-order consciousness implies that mechanisms underlying putative primary 360 conscious states might be distinct from, though possibly overlapping with, mechanisms 361 allowing its accurate report, such that absence of evidence need not be evidence of 362 absence in regard to animal consciousness. 363

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364 Within this framework, we find that birds exhibit rich cognitive and behavioral 365 capabilities consistent with conscious states, including working memory, social learning, 366 planning, and possibly even insight during problem solving. These capabilities are 367 complemented by substantial anatomical homologies and functional similarities with 368 mammals in the thalamocortical systems that are associated with consciousness. The 369 case for cephalopod molluscs is currently much less clear. However, abundant evidence 370 of sophisticated learning and memory faculties and rich behaviors, as well as early 371 indications from studies of cephalopod neurophysiology, suggest at least the possibility 372 of conscious states. 373 374 Given profound gaps that remain in the neuroanatomical characterization of both 375 subphyla, many basic questions remain concerning the existence, form, and prevalence of 376 non-mammalian consciousness (see Outstanding Questions). Future progress in 377 addressing these questions will require elaboration of behavioral paradigms designed to 378 assess complex discriminatory behavior associated with consciousness. Vocal learning in 379 birds provides a particularly promising avenue for achieving this objective (Box 1). In all 380 cases, theoretical developments are necessary to facilitate the transition from correlation to causal explanation 14. Such a transition will allow attribution of animal consciousness 381 382 to be based causally on neural properties rather than on indirect behavioral report. 383 Finally, we note that work on animal consciousness may help in assessing consciousness 384 in humans incapable of report, including infants and patients in vegetative and minimally 385 conscious states. 386 387 Glossary 388 389 Accurate report is a first-person account of what an individual is experiencing, made 390 without the attempt to mislead. Accurate report, which can be given through language or 391 related varieties of voluntary response, has been critical in the investigation of conscious 392 states in humans. In animals without the faculty of natural language, forms of behavioral 393 report acting through other motor channels might be examined to determine the possible 394

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presence of high-order discriminations suggesting conscious states. 395 396 Binocular rivalry occurs when the two eyes are each simultaneously presented with a 397 different image. Rather than seeing both images superimposed on one another, the 398 subject sees one image first, then the other, in an alternating sequence. For example, if 399 one eye is presented with parallel vertical stripes and the other with horizontal parallel 400 stripes, rather than seeing an overlapping ‘weave’ of vertical and horizontal stripes, the subject sees first one orientation of stripes, then the other 83. 401 402 403 Explanatory correlates of consciousness. Conventional approaches within 404 consciousness science have emphasized the search for so-called ‘neural correlates of 405 consciousness’: neural activity having privileged status in the generation of conscious experience 7. However, the transition from correlation to explanation requires an 406 407 explanation of how particular neural correlates account for specific properties of 408 consciousness. Searches for explanatory correlates of consciousness attempt to provide this link 11 14. 409 410 411 Primary consciousness refers to the experience of a multimodal scene composed of 412 basic perceptual and motor events. Primary consciousness is sometimes called perceptual 413 or phenomenal consciousness, and it may be present in animals without true language. 414 By contrast, higher-order consciousness involves the referral of the contents of primary 415 consciousness to interpretative semantics, including a sense of self and, in more advanced forms, the ability to explicitly construct past and future narratives 3. The presence of 416 417 higher order consciousness or metacognition should not be assumed to be necessary for 418 the ascription of primary consciousness, though it may be constitutively required for 419 advanced forms of self-consciousness and consciousness of consciousness (Box 2). 420 421 Transitive inference is the ability to connect two or more separate relations, and is 422 widely regarded as a fundamental process in reasoning. Such abilities have been 423 demonstrated in certain birds. For example, in experiments involving the relative ranking 424 of objects presented in pairs, pigeons were able to determine that B>D after they had 425

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separately learned that A>B, B>C, C>D, and D>E, while great tits have been observed to deduce complex social dominance rankings 30. 426 427 428

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[Show abstract][Hide abstract]ABSTRACT:
The interdisciplinary researches for a scientific explanation of consciousness constitute one of the most ex-citing challenges of contemporary science. However, although considerable progress has been made in the neurophysiology of states of consciousness such as sleep/waking cycles, investigation of subjective and ob-jective nature of consciousness contents raises still serious difficulties. Based on a wide range of analysis and experimental studies, approaches to modeling consciousness actually focus on both philosophical, non-neural and neural approaches. Philosophical and non-neural approaches include the naturalistic dualism model of Chalmers, the multiple draft cognitive model of Dennett, the phenomenological theory of Varela and Maturana, and the physics-based hypothesis of Hameroff and Penrose. The neurobiological approaches in-clude the neurodynamical model of Freeman, the visual system-based theories of Lamme, Zeki, Milner and Goodale, the phenomenal/access hypothesis of Block, the emotive somatosensory theory of Damasio, the synchronized cortical model of Llinas and of Crick and Koch, and the global neurophysiological brain model of Changeux and Edelman. There have been also many efforts in recent years to study the artificial intelli-gence systems such as neurorobots and some supercomputer programs, based on laws of computational ma-chines and on laws of processing capabilities of biological systems. This approach has proven to be a fertile physical enterprise to check some hypothesis about the functioning of brain architecture. Until now, however, no machine has been capable of reproducing an artificial consciousness.

[Show abstract][Hide abstract]ABSTRACT:
From January 2013 scientific projects involving cephalopods became regulated by Directive 2010/63/EU, but at present there is little guidance specifically for cephalopods on a number of key requirements of the Directive, including: recognition of pain, suffering and distress and implementation of humane end-points; anaesthesia and analgesia, and humane killing. This paper critically reviews these key areas prior to the development of guidelines and makes recommendations, including identifying topics for further research. In particular: a) Evidence on how cephalopods might experience pain is reviewed; and a draft scheme of behavioural and physiological criteria for recognising and assessing pain, suffering and distress in cephalopods used in scientific procedures is presented and discussed. b) Agents and protocols currently used for general anaesthesia and analgesia are evaluated. Magnesium chloride, ethanol and clove oil are the most frequently used agents, but their efficacy and potential for induction of aversion need to be systematically investigated, according to the species of cephalopod and factors such as body weight, sex and water temperature. Means of sedating animals prior to anaesthesia should be investigated. Criteria for assessing depth of anaesthesia, including depression of ventilation, decrease in chromatophore tone (paling), reduced arm activity, tone and sucker adhesiveness, loss of normal posture and righting reflex, and loss of response to a noxious stimulus, are discussed. c) Analgesia should be provided for cephalopods used in scientific procedures, whenever this would be the case for vertebrates. However, research is needed to evaluate effective agents and administration routes for cephalopods. d) Techniques for local anaesthesia need to be defined and evaluated. e) Currently used methods of killing and criteria for confirmation of death in cephalopods are evaluated. Based on present knowledge, a protocol for humane killing of cephalopods is proposed. However, further evaluation is needed, along with development of humane methods of killing that will not compromise study of the brain. On humane grounds: i. mechanical (as opposed to chemical) methods of killing should not be used on conscious cephalopods (unless specifically authorised by the national competent authority); and ii. hatchlings and larvae should be killed by overdose of anaesthetic and not by immersion in tissue fixative.

[Show abstract][Hide abstract]ABSTRACT:
Consciousness has long been viewed as a mystery, scientifically inaccessible because of its elusive nature with subjectivity at its core. Attitudes have changed, however, during the last two decades. Hypotheses, frameworks and careful (but incomplete and only partial) theories have been put forward and the general perspective now is one of moderate optimism. The aim of this article is not to extensively review the broad and varied literature, but to introduce the interested but uninitiated reader to this heterogeneous topic. To this end and after a short introduction including definition issues and a brief history, consciousness’ distinct philosophical and neuroscientific components are highlighted by examples. Philosophically, David Chalmers’ dissection of the problems of consciousness and his nonreductionistic viewpoint is set against Daniel Dennett’s no-nonsense approach. Neuroscientifically, the emphasis is on a recently developed theory called theGlobal Neuronal Workspace. Functional and evolutionary aspects of consciousness are also discussed.
Ons bewustzijn wordt vaak afgeschilderd als een mysterie, niet in de laatste plaats omdat het zowel deelneemt aan de wereld als deze tegelijkertijd bevat en een duidelijke subjectieve kant heeft. Onderzoek ernaar begeeft zich op de grens van filosofie, psychologie en (neuro) biologie en kent dus veel invalshoeken en veel meningen. Het is werk in uitvoering, vol hypothesen en raamwerken zonder een duidelijke, dominante theorie. In dit artikel vat ik, middels voorbeelden uit de filosofie en de biologische psychologie, de huidige stand van zaken samen.